Methods for providing spaced lithography features on a substrate by self-assembly of block copolymers

ABSTRACT

A method is disclosed for forming a row of mutually spaced lithography features on a substrate, such as contact electrodes for a NAND device. The method involves forming and/or using a narrow slot over the substrate defined between the edge of a hard mask layer and a side wall of a trench in a resist layer overlying the edge and the substrate. A self-assemblable block copolymer is deposited and ordered in the trench for use as a further resist for patterning the substrate along the slot. The method allows for a sub-resolution contact array to be formed using UV lithography by overlapping the trench with the hard mask edge to provide the narrow slot in which the contact electrodes may be formed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application61/636,346, which was filed on Apr. 20, 2012 and which is incorporatedherein in its entirety by reference.

FIELD

The present invention relates to a method of forming mutually spacedlithography features in a row, or rows, on a substrate, by use ofself-assembly of a block copolymer over a slot provided on thesubstrate. The method may be useful for forming a contact electrodearray for a NAND memory device.

BACKGROUND

In lithography for device manufacture, there is an ongoing desire toreduce the size of features in a lithographic pattern in order toincrease the density of features on a given substrate area. Patterns ofsmaller features having critical dimensions (CD) at nano-scale allow forgreater concentrations of device or circuit structures, yieldingpotential improvements in size reduction and manufacturing costs forelectronic and other devices. In photolithography, the push for smallerfeatures has resulted in the development of technologies such asimmersion lithography and extreme ultraviolet (EUV) lithography.

So-called imprint lithography generally involves the use of a “stamp”(often referred to as an imprint template) to transfer a pattern onto asubstrate. An advantage of imprint lithography is that the resolution ofthe features is not limited by, for example, the emission wavelength ofa radiation source or the numerical aperture of a projection system.Instead, the resolution is mainly limited to the pattern density on theimprint template.

For both photolithography and for imprint lithography, it is desirableto provide high resolution patterning of surfaces, for example of animprint template or of other substrates, and chemical resists may beused to achieve this.

The use of self-assembly of a block copolymer (BCP) has been consideredas a potential method for improving the resolution to a better valuethan obtainable by prior art lithography methods or as an alternative toelectron beam lithography for preparation of imprint templates.

A self-assemblable block copolymer is a compound useful innanofabrication because it may undergo an order-disorder transition oncooling below a certain temperature (order-disorder transitiontemperature T_(OD)) resulting in phase separation of copolymer blocks ofdifferent chemical nature to form ordered, chemically distinct domainswith dimensions of tens of nanometres or even less than 10 nm. The sizeand shape of the domains may be controlled by manipulating the molecularweight and composition of the different block types of the copolymer.The interfaces between the domains may have a line width roughness ofthe order of 1-5 nm and may be manipulated by modification of thechemical compositions of the blocks of the copolymers.

The feasibility of using thin films of block copolymers asself-assembling templates was demonstrated by Chaikin and Register, etal., Science 276, 1401 (1997). Dense arrays of dots and holes withdimensions of 20 nm were transferred from a thin film ofpoly(styrene-block-isoprene) to a silicon nitride substrate.

A block copolymer comprises different blocks, each comprising one ormore identical monomers, and arranged side-by side along the polymerchain. Each block may contain many monomers of its respective type. So,for instance, an A-B block copolymer may have a plurality of type Amonomers in the (or each) A block and a plurality of type B monomers inthe (or each) B block. An example of a suitable block copolymer is, forinstance, a polymer having covalently linked blocks of polystyrene (PS)monomer (hydrophobic block) and polymethylmethacrylate (PMMA) monomer(hydrophilic block). Other block copolymers with blocks of differinghydrophobicity/hydrophilicity may be useful. For instance a tri-blockcopolymer such as (A-B-C) block copolymer may be useful, as may analternating or periodic block copolymer e.g. [-A-B-A-B-A-B-]_(n), or[-A-B-C-A-B-C]_(m) where n and m are integers. The blocks may beconnected to each other by covalent links in a linear or branchedfashion (e.g., a star or branched configuration).

A block copolymer may form many different phases upon self-assembly,dependent upon the volume fractions of the blocks, degree ofpolymerization within each block type (i.e. number of monomers of eachrespective type within each respective block), the optional use of asolvent and surface interactions. When applied in a thin film, thegeometric confinement may pose additional boundary conditions that maylimit the phases formed. In general spherical (e.g. cubic), cylindrical(e.g. tetragonal or hexagonal) and lamellar phases (i.e. self-assembledphases with cubic, hexagonal or lamellar space-filling symmetry) arepractically observed in thin films of self-assembled block copolymers,and the phase type observed may depend upon the relative molecularvolume fractions of the different polymer blocks. For instance, amolecular volume ratio of 80:20 will provide a cubic phase ofdiscontinuous spherical domains of the low volume block arranged in acontinuous domain of the higher volume block. As the volume ratioreduces to 70:30, a cylindrical phase will be formed with thediscontinuous domains being cylinders of the lower volume block. At50:50 ratio, a lamellar phase is formed. With a ratio of 30:70, aninverted cylindrical phase may be formed and at a ratio of 20:80, aninverted cubic phase may be formed.

Suitable block copolymers for use as a self-assemblable polymer include,but are not limited to, poly(styrene-b-methylmethacrylate),poly(styrene-b-2-vinylpyridone), poly(styrene-b-butadiene),poly(styrene-b-ferrocenyldimethylsilane), poly(styrene-b-ethyleneoxide),poly(ethyleneoxide-b-isoprene). The symbol “b” signifies “block”Although these are di-block copolymer examples, it will be apparent thatself-assembly may also employ a tri-block, tetrablock or othermulti-block copolymer.

The self-assembled polymer phases may orient with symmetry axessubstantially parallel or perpendicular to the substrate and lamellarand cylindrical phases are interesting for lithography applications, asthey may provide a resist to form line and space patterns and holearrays, respectively, when oriented with their domains lyingside-by-side on a substrate, and may provide good contrast when one ofthe domain types is subsequently etched.

It will be understood a block copolymer comprising two or more differingblock copolymer molecule types may be used for self-assembly.

Two methods used to guide or direct self-assembly of a polymer, such asa block copolymer, onto a surface are graphoepitaxy and chemicalpre-patterning, also called chemical epitaxy. In the graphoepitaxymethod, self-organization of block copolymer is guided by topologicalpre-patterning on the substrate. Lamellar self-assembled block copolymercan form substantially parallel linear patterns with adjacent lines ofthe different polymer block domains in the enclosures or trenchesdefined by one or more side walls of the graphoepitaxy template. Forinstance if the block copolymer is a di-block copolymer with A and Bblocks within the polymer chain, where A is hydrophilic and B ishydrophobic in nature, the A blocks may assemble into domains formedadjacent to a side-wall of a trench if the side-wall is also hydrophilicin nature. Resolution may be improved over the resolution of thegraphoepitaxy template by a side wall being spaced to fit severaldomains of the block copolymer side-by-side. For hexagonal or tetragonal(cylindrical) ordered patterns, the graphoepitaxy features may bepillars standing in place of cylindrical domains of the ordered patternof the block copolymer.

In the chemical pre-patterning method (referred to herein as chemicalepitaxy), the self-assembly of block copolymer domains is guided by achemical pattern (i.e. a chemical epitaxy template) on the substrate.Chemical affinity between the chemical pattern and at least one of thetypes of copolymer blocks within the polymer chain may result in theprecise placement (also referred to herein as “pinning”) of one of thedomain types onto a corresponding region of the chemical pattern on thesubstrate. For instance if the block copolymer is a di-block copolymerwith A and B blocks, where A is hydrophilic and B is hydrophobic innature, and the chemical epitaxy pattern may comprise a hydrophobicregion on a hydrophilic surface, the B domain may preferentiallyassemble onto the hydrophobic region. As with the graphoepitaxy methodof alignment, the resolution may be improved over the resolution of thepatterned substrate by the block copolymer pattern subdividing thespacing of the pre-patterned features on the substrate (so-calleddensity or pitch multiplication). As was the case with graphoepitaxy,chemical pre-patterning is not limited to a linear pre-pattern; forinstance the chemical epitaxy template may be in the form of a 2-D arrayof dots suitable as a pattern for use with a cylindrical (e.g. hexagonalor square pattern) phase-forming block copolymer. Graphoepitaxy andchemical pre-patterning may be used, for instance, to guide theself-organization of lamellar or cylindrical phases, so that thedifferent domain types are arranged side-by-side on a surface of asubstrate.

Typically, the height of features of a graphoepitaxy template may be ofthe order of the thickness of the block copolymer layer to be ordered,so may be, for instance, from about 20 nm to about 150 nm whereas for achemical epitaxy template, the height difference between adjacentregions of a chemical epitaxy template will typically be less than about15 nm, say less than about 10 nm or even less than about 5 nm in orderto reduce or minimize likelihood of defect formation.

SUMMARY

In a process to implement the use of block copolymer self-assembly innanofabrication, a substrate may be modified with a neutral orientationcontrol layer, as part of the chemical pre-pattern or graphoepitaxytemplate, to induce the preferred orientation of the self-assemblypattern in relation to the substrate. For some block copolymers used inself-assemblable polymer layers, there may be a preferential interactionbetween one of the blocks and the substrate surface that may result inorientation. For instance, for a polystyrene(PS)-b-PMMA block copolymer,the PMMA block will preferentially wet (i.e. have a high chemicalaffinity with) an oxide surface and this may be used to induce theself-assembled pattern to lie oriented substantially parallel to theplane of the surface. Perpendicular orientation may be induced, forinstance, by depositing a neutral orientation layer onto the surfacerendering the substrate surface neutral to both blocks, in other wordsthe neutral orientation layer has a similar chemical affinity for eachblock, such that both blocks wet the neutral orientation layer at thesurface in a similar manner. By “perpendicular orientation” it is meantthat the domains of each block will be positioned side-by-side at thesubstrate surface, with the interfacial regions between adjacent domainsof different blocks lying substantially perpendicular to the plane ofthe surface.

A neutral surface for use in chemical epitaxy and graphoepitaxy isparticularly useful. It may be used on surfaces between specificorientation regions of an epitaxy template. For instance in a chemicalepitaxy template to align a di-block copolymer having A and B blocks,where A is hydrophilic and B is hydrophobic in nature, the chemicalpattern may comprise hydrophobic pinning sites with a neutralorientation region between the hydrophobic sites. The B domain maypreferentially assemble onto the hydrophobic pinning sites, with severalalternating domains of A and B blocks aligned over the neutral regionbetween the specific (pinning) orientation regions of the chemicalepitaxy template.

For instance in a graphoepitaxy template to align such a di-blockcopolymer the pattern may comprise hydrophobic resist features aspillars or side-walls with a neutral orientation region between thehydrophobic resist features. The B domain may preferentially assemblealongside the hydrophobic resist features, with several alternatingdomains of A and B blocks aligned over the neutral orientation regionbetween the pinning resist features of the graphoepitaxy template.

A neutral orientation layer may, for instance, be created by use ofrandom copolymer brushes which are covalently linked to the substrate byreaction of a hydroxyl terminal group, or some other reactive end group,to oxide at the substrate surface. In other arrangements for neutralorientation layer formation, a crosslinkable random copolymer or anappropriate silane (i.e. molecules with a substituted reactive silane,such as a (tri)chlorosilane or (tri)methoxysilane, also known as silyl,end group) may be used to render a surface neutral by acting as anintermediate layer between the substrate surface and the layer ofself-assemblable polymer. Such a silane based neutral orientation layerwill typically be present as a monolayer whereas a crosslinkable polymeris typically not present as a monolayer and may have a layer thicknessof typically less than or equal to about 40 nm, or less than or equal toabout 20 nm. The neutral orientation layer may, for instance, beprovided with one or more gaps therein to permit one of the block typesof the self-assemblable layer to come into direct contact with thesubstrate below the neutral orientation layer. This may be useful foranchoring, pinning or aligning a domain of a particular block type ofthe self-assemblable polymer layer to the substrate, with the substratesurface acting as a specific orientation feature.

A thin layer of self-assemblable block copolymer may be deposited onto asubstrate having a graphoepitaxy or chemical epitaxy template as set outabove. A suitable method for deposition of the self-assemblable polymeris spin-coating, as this process is capable of providing a well defined,uniform, thin layer of self-assemblable polymer. A suitable layerthickness for a deposited self-assemblable polymer film is approximately10 to 100 nm. Following deposition of the block copolymer film, the filmmay still be disordered or only partially ordered and one or moreadditional steps may be needed to promote and/or complete self-assembly.For instance, the self-assemblable polymer may be deposited as asolution in a solvent, with solvent removal, for instance byevaporation, prior to self-assembly.

Self-assembly of a block copolymer is a process where the assembly ofmany small components (the block copolymer) results in the formation ofa larger more complex structure (the nanometer sized features in theself-assembled pattern, referred to as domains in this specification).Defects arise naturally from the physics controlling the self-assemblyof the polymer. Self-assembly is driven by the differences ininteractions (i.e. differences in mutual chemical affinity) between A/A,B/B and A/B (or B/A) block pairs of an A-B block copolymer, with thedriving force for phase separation described by Flory-Huggins theory forthe system under consideration. The use of chemical epitaxy orgraphoepitaxy may greatly reduce defect formation.

For a polymer which undergoes self-assembly, the self-assemblablepolymer will exhibit an order-disorder temperature T_(OD). T_(OD) may bemeasured by any suitable technique for assessing the ordered/disorderedstate of the polymer, such as differential scanning calorimetry (DSC).If layer formation takes place below this temperature, the moleculeswill be driven to self-assemble. Above the temperature T_(OD), adisordered layer will be formed with the entropy contribution fromdisordered A/B domains outweighing the enthalpy contribution arisingfrom favorable interactions between neighboring A-A and B-B block pairsin the layer. The self-assemblable polymer may also exhibit a glasstransition temperature T_(g) below which the polymer is effectivelyimmobilized and above which the copolymer molecules may still reorientwithin a layer relative to neighboring copolymer molecules. The glasstransition temperature is suitably measured by differential scanningcalorimetry (DSC).

Defects formed during ordering as set out above may be partly removed byannealing. A defect such as a disclination (which is a line defect inwhich rotational symmetry is violated, e.g. where there is a defect inthe orientation of a director) may be annihilated by pairing with otheranother defect or disclination of opposite sign. Chain mobility of theself-assemblable polymer may be a factor for determining defectmigration and annihilation and so annealing may be carried out at atemperature where chain mobility is high but the self-assembled orderedpattern is not lost. This implies temperatures up to a few ° C. belowthe order/disorder temperature T_(OD) for the polymer.

Ordering and defect annihilation may be combined into a single annealingprocess or a plurality of processes may be used in order to provide alayer of self-assembled polymer such as block copolymer, having anordered pattern of domains of differing chemical type (of domains ofdifferent block types), for use as a resist layer for lithography.

In order to transfer a pattern, such as a device architecture ortopology, from the self-assembled polymer layer into the substrate uponwhich the self-assembled polymer is deposited, typically a first domaintype will be removed by so-called breakthrough etching to provide apattern of a second domain type on the surface of the substrate with thesubstrate laid bare between the pattern features of the second domaintype.

Following the breakthrough etching, the pattern may be transferred byso-called transfer etching using an etching means which is resisted bythe second domain type and so forms recesses in the substrate surfacewhere the surface has been laid bare.

It would be desirable to have a process and method to form mutuallyspaced lithography features along a substrate by use of self-assembly ofa block copolymer to form a single row, or rows, of spaced elongatedomains along a portion of a substrate. In particular, such a method isdesirable, for example, for forming a contact electrode array for a NANDmemory device by using the spaced elongate domains as resist featuresfor patterning of the substrate.

It is also desirable that the pattern features should be of small size(width or diameter of say about 20 nm or less) and that the spacingbetween adjacent features should be as small as possible—say having aperiodic spacing of about 50 nm or less.

It is desirable, for example, to provide a simple method for providingsuch lithography features on a substrate surface. It is desirable, forexample, to provide a self-assembled layer of block copolymer forsubsequent use as a resist layer suitable for use in device lithographyto form a row of mutually spaced elongate features. It is desirable, forexample, to provide a method using photolithography, for instance withactinic radiation such as UV or DUV radiation, to form a template fordirecting self-assembly of the block copolymer to form such a row oflithography features.

It is desirable, for example, to provide mutually spaced elongatelithography features with small pattern feature size and spacingcompared to prior mutually spaced elongate lithography features preparedusing resist-based UV photolithography.

In an aspect of the invention, there is provided a method of forming arow of mutually spaced lithography features on a substrate, the methodcomprising

providing a hard mask layer on the substrate, the hard mask layerdefining an edge,

providing a resist layer on the substrate overlying the edge,

forming a trench through the resist layer, by removal of a selectedportion of the resist layer, aligned such that the trench has a lengthlying substantially parallel to the edge, the trench having opposedside-walls of resist and a base including the edge, a portion of thehard mask layer and a portion of the substrate, wherein the edge and aside-wall of the trench define a slot over the substrate, the slothaving a width less than a width of the trench,

providing a layer self-assemblable block copolymer, having first andsecond blocks, in the trench,

causing the block copolymer to self-assemble to give an ordered layer inthe trench, wherein the block copolymer is adapted to form the orderedlayer comprising a row of first domains of first block, self-assembledside-by-side in the slot, alternating with a second domain of the secondblock, and

using the ordered layer of block copolymer as a further resist layer foretching the row of mutually spaced lithography features along the sloton the substrate.

The following features are applicable to all the various aspects of theinvention where appropriate. When suitable, combinations of thefollowing features may be employed as part of the embodiments of theinvention, for instance as set out in the claims. An embodiment of theinvention is particularly suitable for use in device lithography. Forinstance, an embodiment of the invention may be of use in patterning adevice substrate directly or may be of use in patterning an imprinttemplate for use in imprint lithography.

The self-assemblable block copolymer may be a block copolymer as set outhereinbefore comprising at least two different block types, referred toas first and second polymer blocks, which are self-assemblable into anordered polymer layer having the different block types associated intofirst and second domain types. The block copolymer may comprise adi-block copolymer and/or tri-block or multi-block copolymers. Analternating or periodic block copolymer may also be used as theself-assemblable polymer. Although only two domain types may bementioned in some of the following aspects and examples, an embodimentof the invention is also applicable to a self-assemblable polymer withthree or more different domain types. The self-assemblable blockcopolymer is desirably a di-block copolymer.

By “chemical affinity”, in this specification, is meant the tendency oftwo differing chemical species to associate together. For instancechemical species which are hydrophilic in nature have a high chemicalaffinity for water whereas hydrophobic compounds have a low chemicalaffinity for water but a high chemical affinity for an alkane. Chemicalspecies which are polar in nature have a high chemical affinity forother polar compounds and for water whereas apolar, non-polar orhydrophobic compounds have a low chemical affinity for water and polarspecies but may exhibit high chemical affinity for other non-polarspecies such as an alkane or the like. The chemical affinity is relatedto the free energy associated with an interface between two chemicalspecies: if the interfacial free energy is high, then the two specieshave a low chemical affinity for each other whereas if the interfacialfree energy is low, then the two species have a high chemical affinityfor each other. Chemical affinity may also be expressed in terms of“wetting”, where a liquid will wet a solid surface if the liquid andsurface have a high chemical affinity for each other, whereas the liquidwill not wet the surface if there is a low chemical affinity. Chemicalaffinities of surfaces may be measured, for instance, by means ofcontact angle measurements using various liquids, so that if one surfacehas the same contact angle for a liquid as another surface, the twosurfaces may be said to have substantially the same chemical affinityfor the liquid. If the contact angles differ for the two surfaces, thesurface with the smaller contact angle has a higher chemical affinityfor the liquid than the surface with the larger contact angle.

By “chemical species” in this specification is meant either a chemicalcompound such as a molecule, oligomer or polymer, or, in the case of anamphiphilic molecule (i.e. a molecule having at least two interconnectedmoieties having differing chemical affinities), the term “chemicalspecies” may refer to the different moieties of such molecules. Forinstance, in the case of a di-block copolymer, the two different polymerblocks making up the block copolymer molecule are considered as twodifferent chemical species having differing chemical affinities.

Throughout this specification, the term “comprising” or “comprises”means including the component(s) specified but not to the exclusion ofthe presence of others. The term “consisting essentially of” or“consists essentially of” means including the components specified butexcluding other components except for materials present as impurities,unavoidable materials present as a result of processes used to providethe components, and components added for a purpose other than achievingthe technical effect of the invention. Typically, a compositionconsisting essentially of a set of components will comprise less than 5%by weight, typically less than 3% by weight, more typically less than 1%by weight of non-specified components. The terms “consist of” or“consisting of” mean including the components specified but excludingthe deliberate addition of other components.

Whenever appropriate, the use of the term “comprises” or “comprising”may also be taken to include the meaning “consist of” or “consistingof”, “consists essentially of” or “consisting essentially of”.

In this specification, when reference is made to the thickness of afeature, the thickness is suitably measured by an appropriate meansalong an axis substantially normal to the substrate surface and passingthrough the centroid of the feature. Thickness may suitably be measuredby a technique such as interferometry or assessed through knowledge ofetch rate.

Wherever mention is made of a “layer” in this specification, the layerreferred to is to be taken to be layer of substantially uniformthickness, where present. By “substantially uniform thickness” is meantthat the thickness does not vary by more than 10%, desirably not morethan 5% of its average value across the layer.

In an embodiment, the method involves providing a hard mask layer on thesubstrate, the hard mask layer defining an edge. The edge will typicallybe a straight edge. A conventional hard mask layer, known in the art,may be employed, and may be of a material such as silicon nitride,silicon oxide, diamond-like carbon, silicon oxynitride, metal, or thelike. The hard mask layer will typically be highly resistant to achemical etch used for the overlying resist layer, and will typically bea layer less than about 20 nm say less than about 10 nm, even about lessthan 5 nm in thickness. Deposition of the hard mask may be achievedusing sputtering, plasma deposition, chemical vapor deposition or thelike, with the edge delineated, for instance, by UV or DUVphotolithography and suitable chemical etching.

A resist layer is provided on the substrate, overlying the edge. Theresist layer may be provided by any suitable method, such as spincoating of a resist solution in a solvent followed by evaporative dryingto provide the resist layer on the substrate. Typically, the resistlayer may be a positive tone resist. By a positive tone resist, is meanta resist which, once exposed to actinic radiation, becomes or isrendered soluble in a solvent so that when subjected to rinsing with thesolvent, one or more exposed portions of the resist are washed awaywhile one or more unexposed portions of the resist remain insoluble inthe solvent. However, an embodiment of the invention may be put intoeffect by use of a negative tone resist (where one or more unexposedportions remain and one or more exposed portions are removed),selectively exposed in an appropriate manner.

A trench is formed through the resist layer by removal of a selectedportion of the resist layer, aligned such that the trench has a lengthlying substantially parallel to the edge. The trench has opposedside-walls of resist, and a base including the edge, a portion of thehard mask layer and a portion of the substrate. A further layer orlayers may be present over the edge and over the substrate, as set outhereinafter. However, the resist over the base of the trench iscompletely removed. This is typically achievable by selective exposureof the resist to actinic radiation, such as UV radiation, followed byremoval of the exposed (positive tone resist) or unexposed (negativetone resist) regions. The actinic radiation may be UV radiation such asDUV (deep UV) or EUV (extreme UV). The selective exposure to actinicradiation may be by patterning of the UV radiation with a lithographyapparatus. A conventional lithographic patterning method such as mask ormaskless UV lithography may be used to provide a desired high resolutionexposure pattern on the resist layer to give the exposed and unexposedregions. Typical DUV lithography is carried out using UV radiationhaving a wavelength of about 193 nm.

The edge and a side-wall of the trench define a slot over the substrate,the slot having a width less than a width of the trench. Suitably, thetrench has a width of about 100 nm or less such as about 50 nm or less(measured normal to the substrate axis at the trenches greatest width).

The substrate may typically be a semiconductor substrate, and maycomprise a plurality of layers forming the substrate. For instance, theoutermost layer of the substrate upon which the resist layer isprovided, may be an ARC (anti-reflection coating) layer. Suitably, theoutermost layer of the substrate may be neutral to the domains of theblock copolymer, by which it is meant that it has a similar chemicalaffinity for each of the domain types of the block copolymer.Alternatively or additionally, a neutral orientation layer may beprovided as an uppermost or outermost surface layer of the substrate, asdescribed hereinafter.

A layer of self-assemblable block copolymer, having first and secondblocks, is then provided in the trench. This may be carried out by spincoating of the block copolymer from a solution followed by removal ofsolvent, for instance. The self-assemblable block copolymer issubsequently caused to self-assemble, for instance by lowering thetemperature to a temperature less than To/d for the block copolymer, togive an ordered layer of self-assembled block copolymer in the trench.The block copolymer is adapted to form the ordered layer comprising arow of first domains of the first block, self-assembled side-by-side inthe slot, alternating with a second domain of the second block.

The ordered layer of self-assembled block copolymer may be used as afurther resist layer for etching the row of mutually spaced lithographyfeatures along the slot on the substrate.

The trench may comprise one or more epitaxy features configured todirect self-assembly of the self-assemblable block copolymer.

The epitaxy feature may comprise a graphoepitaxy template. Thegraphoepitaxy template may comprise one or more recesses or one or morebuttresses of a side-wall of the trench. In a further suitablearrangement, the graphoepitaxy template may comprise a transverse wallof the trench, having a face with a higher chemical affinity for one ofthe first and second domains than for the other of the first and seconddomains, the transverse wall lying across the trench with the facesubstantially normal to the substrate and substantially normal to thesubstrate axis. The transverse wall may be an end wall of the trench.The transverse wall, buttress or recess may be formed during the sameprocess used to form the trench, or may be provided in a separateprocess step (such as conventional UV, DUV, EUV or electron beamlithography).

Alternatively or additionally, the epitaxy feature may comprise achemical epitaxy template, such as a chemical epitaxy templatecomprising one or more pinning stripes on the base of the trench, thestripe lying across the trench, on the substrate, substantially normalto the substrate axis, and the stripe having a higher chemical affinityfor one of the first and second domains than for the other of the firstand second domains. Such a chemical epitaxy template may be depositedusing a conventional DUV or EUV or electron beam lithography technique,such as are known in the art, prior to deposition of the resist layerused for forming the trench. Alternatively, such chemical epitaxytemplate may be put in place after the trench has been formed but beforeproviding the block copolymer into the trench. It will be understoodthat multiple, mutually spaced, substantially parallel pinning stripesmay be provided. Typically, such a chemical epitaxy template maycomprise narrow pinning stripes spaced apart by neutral regions Thepatterned chemical epitaxy template may have the same periodicity (i.e.unit cell pitch) as the self-assembled lamellar block copolymer that itis intended to direct during self-assembly, or the periodic spacingbetween adjacent pinning sites will correspond to a plurality of unitcells, say 2 or 3 unit cells, for the self-assembled polymer. Thisallows for the effect known as density multiplication (sometimes alsoreferred to as pitch multiplication).

An embodiment of the method may involve the self-assemblable blockcopolymer being adapted to form an ordered layer having first,discontinuous domains of the first block in a hexagonal or square arrayalternating with a second continuous domain of the second blocktherebetween. Suitably, only a single row of first, discontinuousdomains of the first block may be arranged to lie over and along theslot.

In a further suitable arrangement, the block copolymer may be adapted toform an ordered layer which is a lamellar ordered layer, wherein thefirst domains are lamellae alternating with second domains which arealso lamellae, the lamellae of the first and second domains orientedwith their planar surfaces lying substantially normal to the substrateand substantially normal to the length of the trench.

A neutral orientation layer may be provided on the base of the trenchoverlying the portion of hard mask layer and the portion of thesubstrate in the trench. In a suitable arrangement, the neutralorientation layer may deposited onto the hard mask layer and thesubstrate prior to provision of the resist layer. The neutralorientation layer may be provided by a method described herein.

The slot may suitably have a width of about 30 nm or less.

The ordered layer of self-assembled block copolymer composition may beused as a further resist layer, for etching the row of mutually spacedlithography features along the slot on the substrate, by selectiveremoval of the first domains followed by subsequent etching of theunderlying substrate with the remaining second domains as an etch mask.The row of mutually spaced lithography features may used to providecontact electrodes for a NAND device.

For instance, the lithography features may be contact pads of a highlyconductive material such as metal, deposited into holes formed using theelongate domains as removed resist features. In order to transfer apattern from the ordered self-assembled polymer layer into thesubstrate, typically the first domains may be removed by so-calledbreakthrough etching to provide a pattern of the second domain on thesurface of the substrate, in the slot, with the substrate laid bare, inthe slot between the pattern features of the second domain.

Following the breakthrough etching, the pattern may be transferred byso-called transfer etching using an etchant which is resisted by thesecond domain and so forms one or more recesses in the substrate surfacewhere the surface has been laid bare. The substrate surface may becovered by a dielectric layer, with one or more holes etched through thedielectric layer, to the underlying substrate. No such transfer etchingwill take place where the hard mask layer shields the substrate, and sothe transfer etching will be restricted to take place within the slot.The holes may then be filled with metal to provide contact electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

Specific embodiments of the invention will be described with referenceto the accompanying Figures, in which:

FIGS. 1A to 1C schematically depict prior art directed self-assembly ofA-B block copolymers onto a substrate by graphoepitaxy and formation ofrelief patterns by selective etching of one domain;

FIGS. 2A to 2C schematically depict prior art directed self-assembly ofA-B block copolymers onto a substrate by chemical epitaxy and formationof relief patterns by selective etching of one domain;

FIGS. 3A and 3B schematically depict plan and side cross-sectional viewsof a substrate undergoing a process according to an embodiment of theinvention; and

FIGS. 4A and 4B schematically depict plan and side cross-sectional viewsof a substrate undergoing a process according to an embodiment of theinvention.

DETAILED DESCRIPTION

The described and illustrated embodiments are to be considered asillustrative and not restrictive in character, it being understood thatonly preferred embodiments have been shown and/or described and that allchanges and modifications that come within the scope of the inventionsas defined in the claims are desired to be protected.

FIG. 1A shows a substrate 1 with a trench 2 formed therein bounded byside walls 3 and a bottom surface 4. In FIG. 1B, a self-assemblable A-Bblock copolymer with, e.g., hydrophilic A blocks and, e.g., hydrophobicB blocks has been deposited into the trench to form a layer 5 withalternating stripes of A and B domains which have deposited as alamellar phase separated into discrete micro-separated periodic domainsduring deposition of the block copolymer. This is referred to asgraphoepitaxy. The type A domains have nucleated adjacent to the a sidewall 3, which is also, e.g., hydrophilic. In FIG. 1C, the type A domainshave been removed by selective chemical etching, leaving the type Bdomains to form a relief pattern in the trench where they may serve as atemplate for subsequent patterning of the bottom surface 4, for instanceby further chemical etching. Selective removal may be achieved, forinstance, by selective photo-degradation or photo-cleavage of a linkingagent between blocks of the copolymer and subsequent solubilization ofone of the blocks. The pitch or wavelength of the self-assembled polymerstructure 5 and the width of the trench 4 are arranged so that a numberof alternating stripes of domains can fit into the trench with a type Adomain against each side wall.

FIG. 2A shows a substrate 10 with a chemical pattern in the form ofpinning stripes 11 which have been chemically formed on the surface 13to provide regions with a higher affinity for the type A blocks of thepolymer. In FIG. 2B, a self-assemblable A-B block copolymer with, e.g.,hydrophilic A blocks and, e.g., hydrophobic B blocks has been depositedonto the surface 13 of substrate 10 to form a lamellar phase layer 12with alternating stripes of A and B domains which have phase separatedinto discrete micro-separated periodic domains during deposition of theblock copolymer. This is referred to as chemical pre-patterning orchemical epitaxy. The type A domains have nucleated atop the pinning ornucleation stripes 11, which are also, e.g., hydrophilic. In FIG. 1C,the type A domains have been removed by selective chemical etching,leaving the type B domains to form a relief pattern on the surface 13where they may serve as a template for subsequent patterning of surface13, for instance by further chemical etching. The pitch or wavelength ofthe self-assembled polymer structure 12 and the spacing of the pinningstripes 11 are arranged so that a number of alternating stripes ofdomains can fit between the pinning stripes 11 with a type A domain atopeach pinning stripe 11.

In the following examples, the di-block copolymer used asself-assemblable polymer in the composition is apoly(styrene-b-methylmethacrylate) block copolymer, denoted by theacronym PS/PMMA, arranged for self-assembly as explained herein.However, the method is also applicable to other self-assemblable blockcopolymers comprising different monomer types.

FIGS. 3A and 3B schematically depict plan and side cross-sectional viewsof a substrate undergoing a process according to an embodiment of theinvention. FIG. 3B is a side cross-sectional view along the section A-Ashown in FIG. 3A.

The Figures show the substrate 20 having a hard mask layer 21 depositedon its upper surface, with a layer of resist 22 provided over thesurface of the substrate 20 and over a portion of the hard mask layer21. A trench has been formed in the resist layer 22, the trenchoverlying a portion of the hard mask layer 21 and also overlying aportion of the bared substrate 20, the bared substrate 20 being presentin a slot 25 located between an edge 23 of the hard mask layer 21 and aside-wall 24 of the resist layer 22 in the trench.

The Figures show the substrate 20 and overlying layers at a stage in theprocess where a self-assemblable block copolymer has been deposited inthe trench and caused to self-assemble into an ordered layer constrainedby the boundaries of the trench. For this embodiment, theself-assemblable block copolymer is adapted to self-assemble into anordered pattern having hexagonal symmetry comprising cylindricaldiscontinuous first domains 26 mutually spaced within a hexagonalpattern having a second continuous domain 27 between the cylindricaldiscontinuous first domains 26. The spacing of the unit cells of thehexagonal ordered pattern is arranged relative to the width of thetrench so that the self-assembly of the block copolymer may take placewithin the constraints of the trench to avoid undue stress in theresulting structure, which may otherwise potentially lead to defects inthe ordered pattern. This is typically achieved by selecting the widthof the trench to correspond to an integral number of unit cells of thehexagonal pattern, taking into account any intermediate zones adjacentto the side-walls where the blocks of the discontinuous domains maydeposit as nucleation of the ordered pattern takes place. Theappropriate trench width may be easily determined by a simpleexperimental method involving varying the trench width and monitoringthe hexagonal pattern deposited, and its unit cell spacings by, forinstance, scanning electron microscopy. In the embodiment shown, theside-walls of the trench have a high chemical affinity for the block ofdiscontinuous domains, while the hard mask layer 21 and substrate 20 areneutral, having a similar chemical affinity for both the first andsecond blocks of the block copolymer. In a modification of thisembodiment, the hard mask layer 21 and substrate 20 may have a neutralorientation layer deposited over their surfaces prior to the depositionof the resist layer 22 and formation of the trench.

In the embodiment shown, the trench has been provided with one or moregraphoepitaxy features by the inclusion of one or more buttresses 28 onone of the side-walls of the trench, formed during the etching of thetrench. The buttress 28 acts to replace one or more of the discontinuousdomains of the ordered pattern as formed by the self-assemblable blockcopolymer, and hence direct the location of nucleation of thediscontinuous domains 26 along the length of the trench.

The width of the slot 25 located between the edge 23 of the hard masklayer 21 and the side-wall 24 of resist layer 22 is arranged to be sothat only one row of discontinuous domains 26 is formed over the slot25. For instance, if the spacing between the centroids of thediscontinuous domains is D, then the width of the slot may suitably beabout D/(3)^(1/2). The width of the slot 25 located between the edge 23of the hard mask layer 21 and the side-wall 24 of resist layer 22 issuitably less than about 30 nm in width, such as about 20 nm in width.

The row of discontinuous domains 26 of the ordered block copolymer layermay subsequently be used as a resist for transfer etching of contactholes into the underlying substrate, along the defined slot 25, asalready described hereinbefore.

FIGS. 4A and 4B schematically depict plan and side cross-sectional viewsof a substrate undergoing a process according to an embodiment of theinvention. FIG. 4B is a side cross-sectional view along the section A-Ashown in FIG. 4A.

As with the embodiment of FIGS. 3A and 3B, the Figures show thesubstrate 20 having a hard mask layer 21 deposited on its upper surface,with a layer of resist 22 provided over the surface of the substrate 20and of a portion of the hard mask layer 21. A trench has been formed inthe resist layer 22, the trench overlying a portion of the hard masklayer 21 and also overlying a portion of the bared substrate 20, thebared substrate 20 being present in a slot 25 located between an edge 23of the hard mask layer 21 and a side-wall 24 of the resist layer 22 inthe trench.

The Figures show the substrate and overlying layers at a stage in theprocess where a self-assemblable block copolymer has been deposited inthe trench and caused to self-assemble into an ordered layer constrainedby the boundaries of the trench. For this embodiment, theself-assemblable block copolymer is adapted to self-assemble into anordered pattern having a lamellar ordered layer wherein the firstdomains are lamellae 28 alternating with second domains 29 which arealso lamellae, the lamellae 28, 29 of the first and second domainsoriented with their planar surfaces lying substantially normal to thesubstrate and substantially normal to the length of the trench. In theembodiment shown, the side-walls of the trench have a neutral chemicalaffinity for the blocks of the first and second domains (i.e. a similarchemical affinity for both the first and second blocks of the blockcopolymer), while the hard mask layer 21 and substrate 20 are also bothneutral, having a similar chemical affinity for both the first andsecond blocks of the block copolymer. In a modification of thisembodiment, the hard mask layer 21 and substrate 20 may have a neutralorientation layer deposited over their surfaces prior to the depositionof the resist layer 22 and formation of the trench.

In a modification to the embodiment shown, the trench may be providedwith one or more chemical epitaxy features by deposition of one or morepinning stripes prior to deposition of the resist layer and trenchformation, on the substrate 20 (also optionally over the hard mask layer21). The pinning stripe may be of a material having a higher chemicalaffinity for one of the domains (28 or 29) of the assembled lamellarblock copolymer, than for the other domain. Hence, the bock copolymerself-assembly may be directed by the enthalpic driving force(minimization of total free energy) directing that domain of the blockcopolymer which has a high chemical affinity for the pinning stripe tobe positioned over the pinning stripe as self-assembly proceeds. Thisprovides the capability to align the positioning of the alternatinglamellae along the slot length.

The width of the slot 25 located between the edge 23 of the hard masklayer 21 and the side-wall 24 of resist layer 22 is suitably less thanabout 30 nm in width, such as about 20 nm in width.

The row of alternating domains 28, 29 of the ordered block copolymerlayer may subsequently be used as a resist for transfer etching ofcontact holes into the underlying substrate, as already describedhereinbefore, for instance by removal of one of the domain types 28leaving the other domain type 29 in place as a transfer etch mask fortransfer of, for example, a row of contact holes, for contact electrodeformation, into the substrate along the defined slot 25.

An embodiment of the invention allows for formation, onto a substrate,of one or more precisely located rows of mutually spaced lithographyfeatures, positioned side-by side along a substrate, using aself-assembled block copolymer to provide features which are henceclosely spaced and small in size.

A particular technical benefit of the method is the ability to use atechnique such as UV or DUV photolithography, having a resolutioncapability of say about 100 nm, to provide a slot over the substrate,the slot having a width considerably less than less than the resolutioncapability of the photolithography method. Typically, the alignmentprecision capabilities of a lithographic apparatus is about 1 to about 5nm, much better than the resolution capabilities, and the method makesuse of this by using the overlap between a broad trench formed bylithography and a hard mask edge formed by lithography to provide a slotof sub-resolution width. The slot may suitably have a width of about 30nm or less and this means that it can be used to isolate a single row ofself-assembled discontinuous domains from an ordered layer ofself-assembled block copolymer aligned in the trench.

An embodiment of the present invention relates to a lithography method.The method may be used in a process for the manufacture of devices, suchas electronic devices and integrated circuits or other applications,such as the manufacture of integrated optical systems, guidance anddetection patterns for magnetic domain memories, flat-panel displays,liquid-crystal displays (LCDs), thin film magnetic heads, organic lightemitting diodes, etc. An embodiment of the invention is also of use tocreate regular nanostructures on a surface for use in the fabrication ofintegrated circuits, bit-patterned media and/or discrete track media formagnetic storage devices (e.g. for hard drives). An embodiment of theinvention is particularly useful for forming contact electrodes for aNAND device.

In particular, an embodiment of the invention is of use for highresolution lithography, where features patterned onto a substrate have afeature width or critical dimension of about 1 μm or less, typicallyabout 100 nm or less or even about 10 nm or less.

Lithography may involve applying several patterns onto a substrate, thepatterns being stacked on top of one another such that together theyform a device such as an integrated circuit. Alignment of each patternwith a previously provided pattern is an important consideration. Ifpatterns are not aligned with each other sufficiently accurately, thenthis may result in some electrical connections between layers not beingmade. This, in turn, may cause a device to be non-functional. Alithographic apparatus therefore usually includes an alignmentapparatus, which may be used to align each pattern with a previouslyprovided pattern, and/or with alignment marks provided on the substrate.

In this specification, the term “substrate” is meant to include anysurface layers forming part of the substrate, or being provided on asubstrate, such as other planarization layers or anti-reflection coatinglayers which may be at, or form, the surface of the substrate, or mayinclude one or more other layers such as those specifically mentionedabove with reference to particular embodiments of the invention.

1. A method of forming a row of mutually spaced lithography features ona substrate, the method comprising: forming a trench through a resistlayer on the substrate, the resist layer overlying an edge of a hardmask layer on the substrate, by removal of a selected portion of theresist layer, aligned such that the trench has a length lyingsubstantially parallel to the edge, the trench having opposed side-wallsof resist and a base including the edge, a portion of the hard masklayer and a portion of the substrate, wherein the edge and a side-wallof the trench define a slot over the substrate, the slot having a widthless than a width of the trench, providing a layer self-assemblableblock copolymer, having first and second blocks, in the trench, causingthe block copolymer to self-assemble to give an ordered layer in thetrench, wherein the block copolymer is adapted to form the ordered layercomprising a row of first domains of the first block, self-assembledside-by-side in the slot, alternating with second domain of the secondblock, and using the ordered layer of block copolymer as a furtherresist layer for etching the row of mutually spaced lithography featuresalong the slot on the substrate.
 2. The method of claim 1, wherein thetrench comprises an epitaxy feature configured to direct self-assemblyof the block copolymer.
 3. The method of claim 2, wherein the epitaxyfeature comprises a recess and/or a buttress of a side-wall of thetrench.
 4. The method of claim 1, wherein the block copolymer is adaptedto form an ordered layer having first, discontinuous domains of thefirst block in a hexagonal or square array alternating with a secondcontinuous domain of the second block therebetween.
 5. The method ofclaim 4, wherein only a single row of first, discontinuous domains ofthe first block is arranged to lie over and along the slot.
 6. Themethod of claim 1, wherein the block copolymer is adapted to form anordered layer which is a lamellar ordered layer wherein the firstdomains are lamellae alternating with second domains which are alsolamellae, the lamellae of the first and second domains oriented withtheir planar surfaces lying substantially normal to the substrate andsubstantially normal to the length of the trench.
 7. The method of claim1, wherein a neutral orientation layer is provided on the base of thetrench overlying the portion of hard mask layer and the portion ofsubstrate in the trench.
 8. The method of claim 7, wherein the neutralorientation layer is deposited onto the hard mask layer and substrateprior to provision of the resist layer.
 9. The method of claim 1,wherein the slot has a width of about 30 nm or less.
 10. The method ofclaim 1, wherein the ordered layer of block copolymer is used as afurther resist layer for etching the row of mutually spaced lithographyfeatures along the slot on the substrate by selective removal of thefirst domains followed by subsequent etching of the underlying substratewith the remaining second domains as an etch mask.
 11. The method ofclaim 1, wherein the row of mutually spaced lithography features is usedto provide contact electrodes for a NAND device.
 12. The method of claim1, further comprising providing the hard mask layer on the substrate.13. The method of claim 1, further comprising providing the resist layeron the substrate.
 14. A method of forming a row of mutually spacedlithography features on a substrate, the method comprising: providing alayer self-assemblable block copolymer, having first and second blocks,in a trench, the trench being through a resist layer on the substrate,the resist layer overlying an edge of a hard mask layer on the substrateand the trench aligned such that the trench has a length lyingsubstantially parallel to the edge, the trench having opposed side-wallsof resist and a base including the edge, a portion of the hard masklayer and a portion of the substrate, wherein the edge and a side-wallof the trench define a slot over the substrate, the slot having a widthless than a width of the trench, and causing the block copolymer toself-assemble to give an ordered layer in the trench, wherein the blockcopolymer is adapted to form the ordered layer comprising a row of firstdomains of the first block, self-assembled side-by-side in the slot,alternating with a second domain of the second block.
 15. The method ofclaim 14, further comprising using the ordered layer of block copolymeras a further resist layer for etching the row of mutually spacedlithography features along the slot on the substrate.
 16. The method ofclaim 14, wherein the trench comprises an epitaxy feature configured todirect self-assembly of the block copolymer.
 17. The method of claim 16,wherein the epitaxy feature comprises a recess and/or a buttress of aside-wall of the trench.
 18. The method of claim 14, wherein the blockcopolymer is adapted to form an ordered layer having first,discontinuous domains of the first block in a hexagonal or square arrayalternating with a second continuous domain of the second blocktherebetween.
 19. The method of claim 14, wherein the block copolymer isadapted to form an ordered layer which is a lamellar ordered layerwherein the first domains are lamellae alternating with second domainswhich are also lamellae, the lamellae of the first and second domainsoriented with their planar surfaces lying substantially normal to thesubstrate and substantially normal to the length of the trench.
 20. Themethod of claim 14, wherein the row of mutually spaced lithographyfeatures is used to provide contact electrodes for a NAND device.